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1: Democritus stated that all matter was made up of tiny particles called atoms. Those atoms are indestructible and unchangeable. They are so small that they can not be divided. | Democritus

2: Believed that all matter was made up of the four elements: Earth, Air, Fire, and Water He also believed that there were four characteristics to these four elements: dryness, hotness, coldness, and moistness. He felt that no matter how many times you cut down a form of matter, there would always be a smaller part of that matter. | Aristotle

3: He believed that since air can be suppressed, there must be space between the atoms. | His greatest contribution, though, was when he developed a law to describe the behavior of gases under pressure. | This became known as Boyle's Law P1V1=P2V2 | Robert Boyle

4: He determined that when different gases reacted, they would always do so in small whole number ratios. | Gay-Lussac's Gas Law: P1T2=P2T1 | Joseph Louis Gay-Lussac

5: He discovered that combustion was a chemical reaction between the burned material and the air. | the total final weight of all the materials burned was exactly equal to the total initial. | Lastly, he discovered oxygen. | Antione Lavoisier

7: He came up with the law of Definite Proportions. | He stated that for copper carbonate to stay copper carbonate, it had to keep the same fixed proportions of copper, carbon and oxygen. | From this, he gathered that all compounds have a fixed certain proportion of the elements. | Joseph Proust

8: -the modern atomic theory published in 1808. -all matter is made of atoms -atoms are indivisible and indestructible. -all atoms of a given atom are identical in mass and properties -compounds are formed by a combination of two or more different kinds of atoms -a chemical reaction is the rearrangement of atoms. | John Dalton

9: -Published his molecular theory in 1811 -equal volumes of gas at the same temperature and pressure contain equal numbers of molecules. -simple gases were not formed of solitary atoms but were instead compound molecules of two or more atoms. -Avogadro's gas law: V1n2=V2n1 where n= number of moles and V= volume | Amedeo | Avogadro

10: In 1853, he discovered the reaction known as Cannizzaro's reaction. It is when an organic compound simultaneously oxidizes and reduces when an alkali is around, and it produces an acid and an alcohol. | In 1860, he reintroduced Avogadro's hypothesis and it became widely accepted. | Stanislao | Cannizzaro

11: In 1869, Mendeleev started to work on his greatest contribution: the periodic table. He arranged the 63 known elements by their atomic weights. He also managed to organize them into groups using their similar characteristics. When there was a gap, he left it open because he predicted that new elements would be found.. Needless to say, he was right. Just in his lifetime, three were found: gallium, scandium, and germanium. | Dmitri Mendeleev

12: In his experiment, Thomson used what is called a cathode ray. A cathode ray is a glass tube with wires inserted in both ends, and then any air that is in it is pumped out. He found that by applying a magnetic field, there was no activity on the electrometer. This meant that the charge had been bent away by the magnet. He deflected the ray and that proved that the charged particles had a negative charge. | Through this experiment, he deduced that cathode rays were made of particles that emanated from within the atoms themselves. | He Developed the "Plum Pudding model: where electrons were pictured as embedded in a positively charged spherical cloud, sort of like raisins in an old-fashioned plum pudding | He reported this discovered in 1897. | J.J. THOMSON

13: He developed the quantum theory. it is where a quantity of energy proportional in magnitude to the frequency of the radiation it represents. Also, it is an analogous discrete amount of any other physical quantity, such as momentum or electric charge. | He discovered a new fundamental constant, called Planck's constant, and for example, used to calculate the energy of a photon. The energy resonator of frequency V is HV where H is a universal constant. | This theory was developed in 1900. | Max Planck

14: -in 1905, he contributed three papers to a German scientific periodical, called Annalen de Physik (Annals of Physics). -They each became the basis of a new branch of physics. -matter and energy was interchangeable. | -in 1905, be develops Special Theory of Relativity. he established the law of mass-energy equivalence: E=mc2 ; energy equals mass times the velocity of light squared. -the above equation was the stepping stone in the development of atomic energy. | -He urged F.D.R to have scientists develop the atomic bomb in 1939. This project became known as the "Manhattan Project." it developed the first nuclear weapon. | Albert Einstein

15: Robert Andrews Millikan | As a result of Thomson not being able to accurately determine the mass or charge, Millikan decided to use the "oil-drop experiment" in 1909. | In doing this, he finally, and accurately, determined that the electron has a negative charge.

16: -He used the gold foil experiment where he fired radioactive particles through minutely thin foils (notably gold) and detecting then using screens coated with zinc sulfide. Rutherford found that although the vast majority of particles passed straight through the foil, approximately 1 in 8000 were deflected leading him to his theory that most of the atom was made up of "empty space." -This was in 1904. | -in 1911, he develops theory of the structure of atoms. -published that the atom has a central positive nucleus surrounded by negative orbiting electrons. -He suggested that the atom had a miniature, dense nucleus surrounded by a cloud of nearly weightless electrons. | Ernest Rutherford

17: -in 1900, observed spontaneous disintegration of radioactive elements into variants he calls "isotopes" or totally new elements. he also discovers "half-life", and makes the initial calculations on energy released during decay. | -in 1912, he proposes a theory of isotopes of elements. | -in 1913, his formulation of the concept of isotopes, which stated that certain elements exist in two or more forms which have different atomic weights but which are indistinguishable chemically. | FREDERICK | SODDY

18: -in 1913, published the results of his measurements of the wavelengths of the x-ray spectral lines of a number of elements which showed that the ordering of the wavelengths of the x-ray emissions of the elements coincided with the ordering of the elements by atomic number. -With the discovery of isotopes of the elements, it became apparent that atomic weight was not the significant player in the periodic law as Mendeleev, Meyers and others had proposed, but rather, the properties of the elements varied periodically with atomic number. When atoms were arranged according to increasing atomic number, the few problems with Mendeleev's periodic table had disappeared. Because of Moseley's work, the modern periodic table is based on the atomic numbers of the elements. | Henry Moseley

19: Neils Bohr | - he suggested that electrons existed at set levels of energy that are at fixed distances from the nucleus. if the atom absorbed energy, the electron would jump to a level further from the nucleus. if it radiated energy, it fell to a level closer to the nucleus. this was in 1912.

20: -he studied the inner core of the atom. -Rutherford and Geiger were partners; the presumed that alpha particles could move through atoms if they could go through thin walls of solids. -he designed a machine that would shoot alpha particles through gold foil onto a screen, where they were observed as tiny flashes of light. it was hard, though, to count thousands of little flashes, so he came up with a solution that was an early version of the "Geiger Counter" an electric machine designed to count released alpha particles. in 1913. | -in 1925, he used his machine to confirm the existence of light quantum, or packets of energy. | Hans Geiger

21: In 1911 | -Rutherford asked Marsden and Geiger to look for alpha particle scattering at large angles, and they were able to, and some even appeared to bounce right back to the source of the particles. -Rutherford said that it was "as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you." -such huge deflections could not be explained by Thomson's model of the atom, where charge was distributed evenly throughout the atom. For such large deflections all the positive charge had to be concentrated in a small mass greater than the mass of the alpha particles. -basically all the charge was in a small mass that was greater than the alpha, meaning the alpha particles are small in mass. | ERNEST MARSDEN

22: FRIEDRICH HUND (right hand side) | -Hund's rule: every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin. -Hund's rules were named after him in 1926. These rules are used to determine which is the term symbol that corresponds to the ground state of a multi-electron atom. | Hund's Rules: 1. The term with maximum multiplicity lies lowest in energy Click on the indicated buttons for more detail. 2. For a given multiplicity, the term with the largest value of L lies lowest in in energy. 3. For atoms with less than half-filled shells, the level with the lowest value of J lies lowest in energy.

23: Robert Wilson | -recruited by Oppenheimer to be the Cyclotron Group Leader, he was part of the Manhattan Project. in 1943. -he headed the team of physicists that developed, built, and operated Fermi National Accelerator Laboratory (Fermilab). -Fermilab advances the understanding of the fundamental nature of matter and energy by providing leadership and resources for qualified researchers to conduct basic research at the frontiers of high energy physics and related disciplines. -cyclotron: a device in which charged atomic and subatomic particles are propelled in spiral paths by the use of a constant magnetic field.

24: Louis de Broglie | In his doctoral dissertation in 1924, Louis de Broglie developed the equation = h/m , which predicts that the wavelength of a particle is inversely proportional to its mass m and velocity where h is Planck's constant | The dual nature of electrons proposed by de Broglie, together with the dual nature of electromagnetic radiation proposed by Max Planck, led to the development of quantum mechanics by the Austrian physicist Erwin Schrodinger in 1926

25: Wolfgang Pauli | Wolfgang Pauli's Principle: -no two electrons in an atom can have identical quantum numbers. they cannot have the same quantum energy, angular momentum magnitude, angular momentum orientation, or orientation of intrinsic spin.

26: Erwin Schröodinger | Published, in 1926, four papers that laid the foundation of the wave-mechanics approach to quantum theory and set forth his wave equation.

27: Werner Heisenberg | He came up with "The Uncertainty Principle." The "uncertainty relation" between the position and the momentum (mass times velocity) of a subatomic particle, such as an electron | Many physicists were slow to accept this principle. Some thought: "Just as a piano string has a fixed tone, so an electron-wave would have a fixed quantum of energy."

28: James Chadwick | in 1932, he discovered the neutron. | It was discovered that when uranium is a target, nuclear fission becomes possible, resulting in nuclear weapons and nuclear power plants.